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Years of caste system belie Indians’ shared ancestry

THE Rigveda, a collection of Sanskrit hymns written around 3500 years ago, doesn’t contain much genetics. It does, however, have the first mention of India’s caste system, and now a genetics study reveals that inbreeding going back thousands of years has led to marked genetic differences between castes. It also shows that India’s many distinct peoples spring from just two ancient populations.

Nick Patterson of the Broad Institute in Cambridge, Massachusetts, and colleagues examined fragments of DNA from 25 groups across India. They included castes and hunter-gatherer tribes, or “scheduled populations”. Each of these groups was genetically distinct, but the …